The present invention relates to door closers in general, and more particularly to improvements in door closers of the type wherein a shaft or an analogous rotary member is biased in a direction to close the door, by way of a motion transmitting device (e.g., a linkage), under the action of an energy storing device and against the opposition of a fluid operated damper.
An automatic door closer of the just outlined character is disclosed, for example, in German Offenlegungsschrift No. 32 34 319 which describes an energy storing device in the form of a spring arranged to displace a reciprocable piston of the hydraulically operated damper. The damper further includes a housing or cylinder for the piston which latter separates a plenum chamber from a second chamber and contains a check valve which can admit pressurized fluid from the second chamber into the plenum chamber. The two chambers are further connected with each other by a flow restrictor. The door closer of the German publication further comprises a stressing device which can prevent the spring from bearing upon the piston of the damper in a direction to close the door through the medium of the shaft. The stressing device is movable by a motor in a direction to cause the spring to store energy and to thus prevent the spring from urging the piston in a sense which would entail a rotation of the shaft in a direction to close the door. The motor for the stressing device is actuated in dependency on the angular position of the door. The arrangement is such that the motor and the stressing device cause the spring to store energy as soon as the door begins to leave its closed position and the motor ensures that the spring is thereupon held out of energy dissipating engagement with the piston as the door continues to move away from the closed position. The motor can act upon the stressing device mechanically, hydraulically or pneumatically. For example, a pressure monitoring device is operatively connected with the motor so as to ensure that the spring does not oppose the movement of the door to its open position. The person who is in the process of opening the door in the customary way must merely exert a force which suffices to shift the piston in its cylinder, to overcome the intertia of the pivotable door panel, to overcome friction between the components of the door hinges, to overcome friction between the elements of the linkage which couples the cylinder to the door frame, to overcome friction between the shaft and its bearings, and to overcome friction between the piston and its cylinder.
A door closer should ensure predictable shutting of the door under normal circumstances as well as under certain exceptional circumstances, e.g., in the event of a fire which entails the establishment of a pronounced pressure differential between the two sides of the door panel in a sense to maintain the door in open position. The magnitude of the pressure differential is the criterion which determines the bias of the aforediscussed spring. This can create problems in door closers of the type wherein the spring is allowed to act upon the piston of the damper with a certain delay following completion of movement of the door from its closed position. Thus, when a person who has just opened the door fails to realize that the door is equipped with a closer (because the movement of the door to its open position necessitates the exertion of a very small force), such person is likely to experience a shock or to be injured (especially a child or a senior or infirm citizen) if such person is abruptly required to resist a very pronounced closing force which is applied by the spring with the aforediscussed delay. For example, the person who has just opened the door can be involved in a conversation and fails to remember or realize that the path for movement of the door back to its closed position should be left unobstructed because the door is about to be closed under the action of a very strong spring.